Color filters so far used in various fields are of the dyed type. Because of their processes of preparation being complicated, however, it has been attempted to prepare color filters by the application of holography.
FIG. 1 is a view for illustrating a conventional process for making color filters by the application of holography.
Referring to FIG. 1, a photosensitive or photographic material 12 is located in opposition to a mirror 13 and a mask 11 having a striped pattern, for instance, is brought into close contact with the material 12. Light incident from above the mask 11 is reflected from the mirror 13 to make an interference fringe, which is in turn recorded in the photographic material 12 to prepare a color filter.
When dirt, dust, etc. are present between the photographic material and the mask in close contact with it, the gap varies, giving rise to the blurring of the mask image. Thus, a serious problem with such a conventional process as shown in FIG. 1 is that a considerable difficulty is encountered in bringing the photographic plate in constantly close contact with the mask in a certain relation.
Even though the close contact is achieved at a certain interval, it is most likely that the mask image may blur due to the thickness of the photographic material itself.
Color filters heretofore used are of the dyed type.
FIG. 2 is a view showing a conventional process for making the dyed type of color filters.
As illustrated, a gelatine layer is first coated on a glass substrate 21 and then subjected to pattern exposure to form a gelatine pattern layer. Next, a dye is fixed to the gelatine pattern layer 23 by treatments with, e.g., tannic acid to make a monochromatic pattern filter. A color filter, which may be in striped, mosaic or other forms, is obtained by repeating the pattern exposure and the formation of the gelatine and dyed pattern layers for each of three colors.
A problem with such a conventional process for making the dyed type of color filters as shown in FIG. 2, however, is that its process of preparation is too complicated to increase the production cost. Another problem is that it is difficult to make a pattern of sufficient resolution.
Still another problem is that a serious difficulty is experienced in getting the overlapping chromatic images in correct registration, since it is required to carry out pattern exposure for each of three colors cyan, magenta and yellow or red, green and blue.
On the other hand, silver salt photography is known as a high-sensitivity photographic technique, in which a photographic image is recorded on a film or the like through a developing step. The image is reproduced with a silver salt emulsion (photographic paper, etc.) or displayed on a cathode ray tube (CRT for short) by the optical scanning of the developed film.
There is also now available an electrophotographic technique. According to this technique, an electrode is deposited onto a photoconductive layer, the photoconductor is electrified on its overall surface by corona electrification in a dark place and then exposed to intense light to make a light-striking region electrically conductive. That region is then rid of charges to optically form an electrostatic latent image on the surface of the photoconductor. Finally, a toner having charges of polarity different from or identical with that of the residual charges is deposited onto the latent image for development. This is primarily used for copying purposes, and cannot be used for photographic purposes due to its low sensitivity. Also, toner development should usually be carried out just after the formation of the latent image, because the retention time or duration electrostatic charges is short.
According to a further technique now available--a TV photographic technique, the original image is picked up by a pickup tube, and the image-carrying information obtained by making use of an optical semiconductor is outputted in the form of electrical signals, which are immediately used to make an image on a CRT. Alternatively, the signals may be recorded on a video tape or the like by magnetic recording hardware for making an image on the CRT at any desired time.
The silver salt photographic technique provides an excellent means for preserving the original image, but needs not only a developing step for making a silver salt image but also sophisticated optical, electrical or chemical processings from hard copying to soft copying (CRT displaying) for the reproduction of the image.
Electrophotography provides a simpler and faster development of the obtained latent image than does the silver salt photographic technique, but is much inferior in the dissociation of a developer, image quality, etc. to the silver salt technique, because the duration of the latent image is very short.
TV photography needs line sequential scanning for outputting or recording the electrical image signals obtained by the pickup tube. The line sequential scanning is performed either by electron beams in the pickup tube or by a magnetic head for video recording. However, this recording technique is much inferior to planar analog recording such as silver salt recording, because its resolution is dependent upon the number of the lines to be scanned.
This is again true of the resolution of a TV photographic system now under development, which makes use of a solid photographic element (CCD, etc.)
The problems associated with these techniques imply that the higher the quality and resolution of the recorded image, the more complicated the processing steps, or the simpler the processing steps, the poorer the storing or memory function, the image quality, etc.
The inventor has applied a patent application (Japanese Patent Application No. 63(1988)-121592 for a process for recording and reproducing electrostatic images, wherein a photographic material comprising a photoconductor layer having an electrode formed on its front surface and a charge carrier medium comprising a charge carrier layer having an electrode formed on its rear surface are located on an optical axis in opposite relation, and the assembly is then exposed to light while applying voltage between both the electrodes to form on the charge carrier medium an electrostatic latent image corresponding to the incident optical image.
According to this process for recording and reproducing electrostatic images, the photographic material is provided by laminating a photoconductive layer on an electrode, and is located in opposition to the charge carrier medium, following by pattern exposure for the photographic plate while voltage is applied between both the electrodes, thereby accumulating imagewise charges in the charge carrier medium. In this instance, a color filter may be located in the optical path in front of the photographic material to make a color image. The color filter may be spaced away from, or made intergral with, the photographic material.
However, much labor and time are required to laminate the color filter individually on the photographic plate.
The present invention seeks to provide a process for preparing a precise color filter by recording a sharp mask image in a photosensitive or photographic material with no need of bringing a mask into precisely close contact with the photographic material.
Another object of this invention is to provide a process for reproducing a color filter which uses a hologram capable of achieving sufficient resolution while dispensing with a photolithographic step, precise alignment or registration, etc.
A further object of this invention is to provide a process for providing an efficient lamination of a filter on a photographic material used in recording electrostatic images.